1. Field of the Invention
This invention relates generally to a dual source power brake booster assembly, and more particularly to an assembly having, in series, an air-vacuum operated booster section and a hydraulic pressure operated booster section.
2. Description of the Prior Art
Conventionally, the booster assembly of the above-mentioned type has been proposed wherein the booster brake pressures are initially obtained by operation of the vacuum booster section without operating the hydraulic booster section, and are then obtained by operation of the hydraulic booster section after the vacuum booster section reaches its limit or run-out condition.
The above assembly is effective to reduce the consumption of vacuum, and an example of such an assembly is illustrated in U.S. Pat. No. 3,935,709. This prior art device has, however, a vacuum actuated power piston which is movable relative to the movement of a hydraulic pressure actuated power piston which is, in turn, arranged integrally with an output member of the assembly, and this arrangement requires a reaction mechanism for each of the vacuum and hydraulic booster sections.
In the above-noted prior art device, the hydraulic booster section must also be provided with a hydraulic reaction mechanism which includes differential hydraulic pressure receiving areas thereby giving the reaction force to the vehicle operator. By this construction, another fluidically actuated means, such as, for example, a power steering gear, may be arranged between a hydraulic pressurized source and the hydraulic reaction mechanism so as not to generate any hydraulic reaction force at the reaction mechanism of the hydraulic booster section when, for example, the power steering gear is actuated. However, this requires a power steering gear which can deliver at least the fluid pressure required by the hydraulic booster section so as to assure the operation of the hydraulic booster even when the power steering gear is in the operating condition.